RU2544889C1 - Method for experimental determination of resistances of transformer windings - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention relates to power industry, namely to measurement of parameters of transformer windings. Essence of the proposed invention consists in the fact that measurement of parameters of three-phase double-winding transformers at short circuit is performed in the beginning at a connection circuit of the primary winding to a triangle and then to a star. Then, as per measured power values of three phases, average linear values of voltage and short circuit current, full short circuit resistance, as well as values of active and reactive short circuit resistance are determined by formulas; besides, phase values of resistance of the primary transformer winding are determined by formulas as well.

EFFECT: improving operating reliability of transformers by receiving an information on their state.

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Description

The invention relates to measuring parameters of transformer windings. A device is known (see RF patent RU 2281522 C1, 2006, [L-1]) for determining the short-circuit impedance of the windings of a three-phase power transformer, containing a three-channel source of controlled alternating voltage and a three-phase impedance meter. Using the above device, the total, active and reactive resistances of the primary and secondary windings of the transformer are not separately determined.

There is a method (see RF patent RU 2364876 C1, 2009, [L-2]) for determining the parameters of a T-shaped equivalent circuit of a three-phase three-winding transformer in operating mode, which consists in the fact that after connecting the high voltage winding to the power source, and windings of medium and low voltage to the loads register for the same time instants instantaneous values of voltages and currents in the windings of all phases. Then, the effective voltage values of all windings and transformation ratios are determined, with the help of which the currents and voltages of the medium and low voltage windings are brought to the high voltage winding circuit. After that, the instantaneous values of the average voltage winding voltages are determined, which are taken equal to the voltages of the magnetization branch of the transformer equivalent circuit. Then, arrays of instantaneous values of the magnetizing current are simultaneously formed as the difference between the instantaneous values of the current in the high voltage winding and the sum of the instantaneous values of the reduced currents of the medium and low voltage windings and the voltage drop across the resistances of the high and low voltage windings as the difference between the instantaneous voltage values of the high voltage winding and the magnetizing branch, respectively , as well as the branches of magnetization and the low voltage on the winding. Next, the effective values of the high voltage winding currents, the magnetizing branches and the reduced current of the low voltage winding are determined from the arrays of instantaneous values of these currents. The losses of active power in the high and low voltage windings and in the magnetization branch are determined as the average values of the instantaneous powers of the corresponding windings over a period, as well as the reactive power losses in the same windings, determining them by arrays of instantaneous values of currents and voltages of the corresponding windings through the area of the current-voltage characteristics of these windings. For all three phases, the active and reactive components of the resistances of the high and low voltage windings and the branches of magnetization are determined from the known current values of currents and the value of losses of active and reactive powers. This invention does not allow to determine the active, reactive and impedance of the transformer medium voltage winding, because the instantaneous reduced value of the electromotive force of the magnetizing branch is taken to be the instantaneous reduced voltage value of the medium voltage winding, that is, the voltage loss in this winding is not taken into account.

The closest in technical essence to the claimed object is a method for determining the parameters of a T-shaped equivalent circuit of a three-phase three-winding transformer in operating mode, described in [L-2]. He is taken as a prototype.

The technical result of the claimed invention is to increase the reliability of transformers by obtaining information about their condition.

The technical result of the invention is achieved due to the fact that the measurement of the parameters of three-phase double-winding transformers in the experience of short circuiting is carried out first with the connection circuit of the primary winding in a triangle, and then in a star. With the equivalent conversion of three identical resistances included in a triangle into a three-beam star, their values decrease by 3 times. Therefore, the resistances of a three-phase double-winding transformer in short circuit experiments are different by a 3-fold decrease in the total, active and reactive resistances of the primary winding when it is connected to a triangle Z _kt1 , r _kt1 , x _kt1 compared to the connection to the star Z _kz1 , r _kz1 , x _kz1 , and the values of the secondary resistances Z _kt2 , r _kt2 , x _kt2 and Z _kz2 , r _kz2 , x _kz2 reduced to the number of turns of the secondary winding remain constant. Since the total, active and reactive short-circuit resistance of a three-phase two-winding transformer are equal to the sum of the corresponding resistances:

Z _ct = Z _ct1 -Z _ct2 ;

Z _KZ = Z _KZ1 + Z _KZ2 ;

r _ct = r _{ct1 +} r _ct2 ;

r _KZ = r _{KZ1 +} r _KZ2 ;

x _ct = x _ct1 + x _ct2 ;

x _KZ = x _KZ1 + x _KZ2 ;

then the total, active and reactive short-circuit resistances obtained on the basis of the experience of short-circuiting a three-phase two-winding transformer with a primary circuit connected to a triangle are 2/3 less than the primary phase phase resistances Z _kp , r _kp , x _kp compared with the corresponding parameters obtained on the basis of the experience of short-circuiting a three-phase two-winding transformer with a connection circuit of the primary winding into a star:

Z _KZ -Z _CT = 2Z _CP / 3;

r _KZ -r _ct = 2r _cp / 3;

x _KZ -x _CT = 2x _CP / 3.

Finally, we have that the total, active and reactive phase short-circuit resistances of the primary winding are one and a half times the difference between the corresponding parameters calculated on the basis of measurements made in the short-circuit experiments of a three-phase double-winding transformer when connecting the primary winding to a star and then to a triangle:

Z _kn = 1.5 (Z _KZ -Z _CT );

r _kp = 1.5 (r _kz -r _kt );

x _kn = 1.5 (x _short -x _ct ).

The invention is illustrated by the drawings shown in Fig. 1 and 2. In this case:

1 - three identical ammeter RA;

2 - two identical PW power meters;

3 - three identical voltmeters PV;

4 - primary winding of a three-phase double-winding transformer connected in a triangle;

5 - secondary winding of a three-phase double-winding transformer connected to a star and short-circuited;

6 - primary winding of a three-phase double-winding transformer connected to a star;

7 - secondary winding of a three-phase double-winding transformer connected to a star and short-circuited.

In Figs. 1 and 2, the secondary windings 5 and 7 of a three-phase two-winding transformer connected to a star are short-circuited. The wires supplying the primary windings, which are connected in a triangle (Fig. 1) and a star (Fig. 2), include three identical ammeter RA 1, two identical wattmeters PW 2 and three identical voltmeters PV 3.

The claimed invention is as follows. In the case of a short circuit, the secondary winding 5 and 7 of a three-phase two-winding transformer connected to a star (Fig. 1 and 2) is short-circuited, and a reduced line voltage U _{k is} applied to the primary winding 4 and 6, at which the primary line current I _k is equal to the rated the value of I _n . For a three-phase two-winding transformer, the short-circuit power of the three phases P _k is determined from the algebraic sum of the readings of two PW 2 wattmeters, and the average values of the linear voltage U _k and linear current I _k are calculated from the readings of three voltmeters PV 3 and ammeters PA 1.

When connecting the primary winding 4 of a three-phase two-winding transformer with a triangle (Fig. 1), the phase parameters of the short circuit:

;short circuit impedance

;

;short circuit resistance

;

.short circuit reactance

.

When connecting the primary winding 6 to the star (Fig. 2), the phase parameters of the short circuit:

;short circuit impedance

;

;short circuit resistance

;

.short circuit reactance

.

Then, the values of the total, active and reactive short-circuit resistances obtained from the short-circuit experience of a three-phase double-winding transformer with the connection circuit of the primary winding into a star are subtracted from the values of the corresponding resistances calculated by connecting the primary winding to a triangle. Further, these differences are increased by 1.5 times, there are phase values of the total, active and reactive resistances of the primary winding:

Z _kn = 1.5 (Z _KZ -Z _CT );

r _kp = 1.5 (r _kz -r _kt );

x _kn = 1.5 (x _short -x _ct ).

The parameters of the full, active and reactive short circuit resistances of the primary winding of three identical single-phase double-winding transformers can be determined similarly experimentally when they are connected in a three-phase group. The parameters of the full, active and reactive short circuit resistances of the secondary winding of a two-winding three-phase transformer and any winding of multi-winding three-phase and single-phase transformers can be determined similarly, turning it into primary.

Bibliography

1. Patent RU 2281522 C1 G01R 31/02 (2006.01). A device for determining the short circuit resistance of the windings of a three-phase transformer with neutral brought to the housing / Mikheev G.M., Fedorov Yu.A., Batalygin S.N., Shevtsov V.M. - Announced on January 11, 2005; publ. 08/10/2006.

2. Patent RU 2364876 C1. G01R 27/02 (2006.01). A method for determining the parameters of a T-shaped equivalent circuit of a three-phase three-winding transformer in operating mode / Goldstein E.I., Prokhorov A.V., Pankratov A.V. - Announced on 05/19/2008; publ. 08/20/2009.

Claims (1)

A method for experimentally determining the resistances of transformer windings by determining the short circuit resistance of a transformer, characterized in that the short-circuit resistance of a three-phase transformer or a group of three identical single-phase transformers is first measured in the case of primary windings connected first to a triangle, and then to a star, then by the measured values of the power of the three phases P _k , the average linear values of the voltage U _k and current I _to short circuit opr they make the full z _ct , z _cc , active r _ct , r _cc and reactive x _ct , x _cc short circuit resistance when connecting the transformer primary winding to a triangle and a star, while calculating by the formulas:
$$z_{\mathrm{to}t}=\sqrt{3}U\mathrm{to}/I\mathrm{to}$$

,
$$z_{\mathrm{to}s}=U\mathrm{to}/(\sqrt{3}I\mathrm{to})$$

,
r _ct = P _c / I _to ² ,
r _KZ = P _to / (3I _to ² ),
$$x_{\mathrm{to}t}=\sqrt{(z_{\mathrm{to}t}^2-r_{\mathrm{to}t}^2)}$$

,
$$x_{\mathrm{to}s}=\sqrt{(z_{\mathrm{to}s}^2-r_{\mathrm{to}s}^2)}$$

,
then the total, active and reactive short-circuit resistances are subtracted when connecting the transformer primary winding to a star and a triangle, then these differences are increased by 1.5 times, and the phase resistances of the transformer primary winding are determined by the formulas:
Z _kn = 1.5 (Z _KZ -Z _CT );
r _kp = 1.5 (r _kz -r _kt );
x _kn = 1.5 (x _short -x _ct ),
where Z _KZ , r _KZ , x _KZ is the total, active and reactive short circuit resistance of the transformer when connecting the primary winding of the transformer to a star; Z _ct r _ct , x _ct is the total, active and reactive short circuit resistance of the transformer when connecting the transformer primary winding to a triangle.

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